Constant current source for the operation of multiple coil systems

ABSTRACT

A constant current source for the operation of multiple coil systems, utilizing a static winding and one or more dynamic windings effective at a common air gap, including a constant operational voltage source, a corrective element between the operation voltage source and static winding, and a current control system operative to control the correcting element, in which a corresponding higher operational voltage is applied to the static winding in the presence of subtractive voltages induced in the static winding as a result of the dynamic winding, with the corresponding higher operational voltage being derived from an independent voltage source or from the charge on one or more capacitors, arranged for charging to the lower operational voltage and adapted to be connected in series to provide a multiple of such voltage.

United States Patent [1 1 Leszke Dec. 4, 1973 1 CONSTANT CURRENT SOURCE FOR THE OPERATION OF MULTIPLE COIL SYSTEMS [75] Inventor: Hans-Hinrich Leszke, Kiel,

Germany [73] Assignee: Dr.-Ing. Rudolf Hell GmbH [22] Filed: Feb. 1, 1973 V 21 Appl. No.: 328,741

[30] Foreign Application Priority Data Feb. 5, 1972 Germany P 22 O5 4688 [52] US. Cl 323/4, 323/6, 323/9, 310/13 C,310/31 TV [51] Int. Cl G05f 1/56, G05f 1/62 [58] Field of Search 315/13 C, 27 TD, 315/31 R, 31 TV; 321/20; 323/4, 6, 9, 38,

[56] References Cited UNITED STATES PATENTS 2,991,407 6/1961 Murphy 323/4 3,350,599 10/1967 Rickling 323/4X Primary Examiner-Gerald Goldberg Attorney-Carlton Hill et al.

[ 5 7 ABSTRACT A constant current source for the operation of multiple'coil systems, utilizing a static winding and one or more dynamic windings effective at a common air gap, including a constant operational voltage source, a corrective element between the operation voltage source and static winding, and a current control system operative to control the correcting element, in which a corresponding higher operational voltage is applied to the static winding in the presence of subtractive voltages induced in the static winding as a result of the dynamic winding, with the corresponding higher operational voltage being derived from an independent voltage source or from the charge on one or more capacitors, arranged for charging to the lower operational voltage and adapted to be connected in series to provide a multiple of such voltage.

11 Claims, 3 Drawing Figures PA-TENTEUBEC 4191s SHEET 2 0F 2 inductive voltage at W72 E 0 volt I static voltage at W72 thresheld operational voltage at emitter of T2 -volt operational voltage at P4 time Fig. 3

. CONSTANT CUR-RENT SOURCE FOR THE OPERATION OF MULTIPLE COILlSYSTEMS BACKGROUND OF TITI-IE INVENTION The invention is directed to a constant current source for the operation of multiple coilsystems employing a static and one or more dynamic windings which are effective at a common air gap,;in which the constant current source includes a constant operational voltage source, a correcting element operatively disposed between the operational .voltage source and the static winding, and with a current control system for effecting control of the correcting element.

Usually a static focusing winding and a dynamic winding are utilized for the focusing of the electron beam of acathode-ray tube, to vary the field in the peripheral areas relatively remote from the icenter of the tube face. As a result of the utilization of a common air gap for both windings, voltages are unavoidably induced in the static winding in the present of current changes in the dynamic winding.

As the number of turns in the static winding is usually much greater than that of the dynamic winding, the voltages induced in the static winding may be greater than the operational voltage applied to the control circuit.

In order to maintain the current :in the static winding constant irrespective of the above conditions it has heretofore been the practice to select an operational voltage of such magnitude that it is greater than any opposing induced voltage peaks which may occur. While it is possible to operate with such high operational voltage, this solution has the disadvantage that a loss of power will result at the correcting element operatively connected between the operational voltage source and the static winding, which loss is proportional to the difference between the operational voltage and the voltage at the two winding terminals of the static winding. Consequently, the power converted :into undesired heat will materially increase with an increase in the operational voltage, withthe ratio becoming even more :unfavorable in the situation where the high induced voltage occurs relatively infrequently.

It is therefore the problem of the present invention to provide an improved system of the type referred to, in which an increased operational voltage is "applied only when required for the balance of induced voltage peaks, with a lower operational voltage being applied in the absence of such peaks.

BRIEF SUMMARY OF THE INVENTION The problem is solved in the present invention by the utilization of a thresholdvalue sensing system which is connected to the static winding and to a thresholdvalue switch whereby the latter will operatively connect the static winding, over the correcting element, with a higher operational voltage in the presence of subtractive voltages induced in the static winding resulting from the presence of the dynamic winding.

It is possible to employ as the higher operational voltage a separate, independent higher operational voltage supply, or one or morecapacitors which are charged by the normal low operational voltage and whose charge voltage can be operatively connected in series with the operational voltage over a cooperable switch when the threshold-value switch is actuated by the presence of an induced voltage peak.

In the event a simple capacitor circuit is insufiicient to provide a suitable high voltage, one or more addi tional capacitors circuits of the same type may be provided, preferably each utilizing a transistor as the switching means for such capacitor.

In apreferred form of the invention, a transistor may be employed as the threshold-value switch and a Zener diode as the sensing means for actuating such transistor.

The invention proceeds from the recognition that current changes in a winding of a multiple-coil system do not immediately cause a corresponding voltage at the terminals of a second magnetically coupled winding, but, due to the inductivity and capacitance of the winding, results following a delay, whereby the second winding behaves as a parallel oscillator circuit which may even overshoot in the opposite direction, assuming a small loss resistance. The relatively slow increase of the induced coil voltage permits the switching over from the normal lower operational voltage to a higher operational voltage for a required short period of time when a predetermined threshold-value is reached at the static winding. Following the expiration of the induced voltage half-wave, the threshhold-value switch will immediately deactivate to return the application of the normal low operational voltage to the static winding. This operation can be repeated as often as desired and presents the advantage that the increased operational voltage is applied when only actually required, whereby the loss at the correcting element of the current control system is increased only very slightly above the value existing under purely static operations.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like characters indicate like or corresponding elements;

FIG. 1 is a schematic circuit diagram of a system according to the invention employing a separate independent higher voltage source;

FIG. 2 is a schematic circuit diagram, similar to FIG. 1 illustrating a further embodiment of the invention in which two capacitors and respective controlling transistors are utilized as a higher voltage source; and

FIG. 3 is a graphic representation of various voltages involved in the operation of the system.

DETAILED DESCRIPTION OF THE INVENTION Referring to the arrangement of FIG. 1 illustrating an example of a system, embodying the invention, for the current supply of a combined static-dynamic focussing system, indicated generally by the numeral 1, which comprises a static winding w, containing a relatively large number of turns, and a dynamic winding w containing a substantially smaller number of turns, with the respective windings being disposed at a common air gap, not illustrated.

A current control system is provided which insures that a constant current will steadily flow through the static winding w such control system being supplied with a constant voltage over terminals P and P and in the example, a negative operational voltage of 40V being supplied at the terminal P The current of the static winding w, flows across the resistance R.;, over winding w transistor T and across the decoupling diode D to the low operational voltage at terminal P A current change occuring at the resistor R thus causes a corresponding current change at the resistor R If a difference arises between the current through the resistor 25 and the current, which flows from P through the resistors R, and R a voltage change will result at the summation point a, of the amplifier A, ie a negative potential will be produced at the inverting input of the amplifier A.

The latter will be amplified, appearing at the outlet a of the control amplifier A with positively increasing potential and will be applied to the base of the transistor T, over the resistor R,,. The collector current of the transistor T, thus will be lowered. As the transistor T, determines the operation of the transistor T the collector current of the latter will likewise be lowered and thereby the current for the static winding w, will likewise be lowered. Such control loop is so designed that an equilibrium of currents will occur under normal static operation, whereby the winding current is proportional to the current through resistors R, and R In the presence of induction voltages, induced in the static winding w, by the dynamic winding W2, the voltage of the static winding w, will be influenced either additively or subtractively, whereby the winding terminal w, becomes either more positive or more negative with respect to its normal static level. If a positive induced voltage occurs at the winding terminal w, this will result in an addition to the lower operational voltage source and will be controlled without difficulty by the control amplifier A (see the positive induced amplitude at the left side of FIG. 3), by effecting an increase in the collector-emitter resistance of the transistor T functioning as a correcting element. The path over a Zener diode D, and a diode D connected in series therewith and which is oppositely poled, is blocked due to the polarity of diode D If however, a negative induced voltage occurs at the winding w, (as illustrated at the right side of FIG. 3) this will cause a subtraction from the lower operational voltage, possibly causing a reduction in the coil current, and in extreme cases even a reverse of the current direction. To prevent this possibilityfmeans are provided for switching over from the lower operational voltage supply (-4OV) to a higher operational voltage supply (-ISOV). Such switching over is initiated when the Zener voltage of the diode D, is reached, such voltage being conducted over diode D and series resistors R to the base of a transistor T functioning as a threshold-value switch. The transistor T following triggering thereof, will so control a transistor T connected over resistor R,,, with the collector of the transistor T that the transistor T, will be conductive. In addition to the above components, base resistor R,, for the transistor T and base resitor R,, for the transistor T are provided.

As the emitter of transistor T is connected with terminal P supplying the higher operational voltage of 150V, conduction oftransistor T, will result in the application of this higher operational voltage to the transistor T, which functions as the correcting element when the transistor T, is rendered conductive. A misapplication of such higher operational voltage with respect to the normal operation voltage supplied to the terminal P of 40V, is prevented by the suitably poled diode D in the supply line.

As soon as the negative induced amplitude decays to a point below the threshold-value of the Zener diode D,, the two transistors T and T, will be blocked and the lower operational voltage of 4OV will be supplied to the emitter of transistor T FIG. 2 illustrates a further embodiment of the invention which in many respect corresponds directly with the circuit of FIG. 1, and accordingly component elements of FIG. 2 are provided with the same reference numerals as corresponding elements illustrated in FIG. 1.

If a positive inductive voltage appears at the winding terminal w the control process will be the same as previously described with respect to the system of FIG. 1.

However, in this arrangement, the low voltage source is operatively connected to the emitter of the transistor T over respective diodes D,, and D,,. The diode D,, is operatively shunted by a capacitor C, and the emittercollector path of a transistor T the collector of which, and thus one side of the capacitor C,, being connected to common by a resistor. The base of the transistor T is operatively connected over a resistor R,,, to the collector of the transistor T In like manner the diode D is operatively shunted by the capacitor C and emittercollector path of the transistor T R,, comprising the base resistor and resistor R,,, connecting the base thereof to the collector of the transistor T Thus, assuming that the transistors T and T are blocked, the capacitors C, and C will be charged to the potential of the low operating voltage appearing at terminal P If a negative induced voltage now appears at the winding terminal W the transistor T, will be rendered conductive in the manner previously described, and as the bases of the two transistors T and T are connected with the collector of the transistor T such transistors likewise will conduct. As the respective capacitors C, and C cannot discharge through the associated, oppositely poled diodes D and D,, the charges on the respective capacitors will be applied in series with the low operational voltage -40V on the emitter of the transistor T and as soon as the negative induced amplitude has decayed below the threshold-value of Zener diode D,, the transistors T T and T, will again be blocked, permitting the capacitors C, and C to recharge.

It will be appreciated that, the in dependence upon the operating parameters involved, merely a single capacitor may be employed, or if desirable additional capacitors over the two illustrated, may be provided circuited in similar manner.

Having thus described my invention it is obvious that although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. A constant current source for the operation of multiple coil systems employing a static winding and at least one dynamic windings, effective at a common air gap, having a constant operational voltage source, a correcting element operatively disposed between the operational voltage source and the static winding, and a current system operative to control the correcting element, comprising a threshold-value switch, thresholdvalue sensing means operatively connected to the static winding and to the threshold value switch, a corresponding higher operative voltage source, said threshold-value switch being operative in the presence of subtractive voltages, induced in the static winding as a result of the presence of the dynamic winding, to connect the static winding with said higher corresponding operational voltage source over said correcting element.

2. A system according to claim 1, wherein the higher operational voltage source is a separate independent operational voltage source.

3. A system according to claim 1, wherein the higher operational voltage source comprises at least one capacitor circuited to be charged by the lower operational voltage, and associated switch means operatively connected to said threshold-value switch, operative, when the latter is actuated, to switch the charge voltage of said capacitor in series with the lower operational voltage source.

4. A system according to claim 3, wherein a plurality of charged capacitors and associated switch means are provided and arranged for connection in series with said lower operational voltage, when said threshold value switch is actuated.

5. A system according to claim 3, wherein said associated switch means comprises a transistor.

6. A system according to claim 4, wherein said associated switch means for the respective capacitors each comprises a transistor.

7. A system according to claim 6, wherein each of said capacitors is circuited to receive said lower operational voltage over an appropriately poled diode, the transistor comprising the switch means associated with each capacitor being operatively connected in series with such capacitor, and such capacitor and cooperable transistor shunting the associated diode, said diodes being operative, when the associated transistors are blocked, to supply the lower operational voltage to said correcting element and to the respective associated capacitors to charge the same, and, when the associated transistors are conductive, to prevent discharge of the associated capacitor other than in series with said operational voltage and said correcting element.

8. A system according to claim 7, wherein said correcting element comprises a transistor operatively connecting said winding, over said diodes, to said lower operational voltage, said threshold-value switch comprising a transistor operatively controlled by said threshold-value sensing means, the latter comprising a Zener diode operatively connecting said winding to said threshold-value transistor.

9. A system according to claim 1, wherein the threshold values switch'comprises a transistor, and the threshold-value sensing means comprises a Zener diode.

10. A system according to claim 2, wherein said independent higher operational voltage source is operatively connected to and controlled by said thresholdvalue switch, and a diode operatively connecting said correcting element to the lower operation voltage source for blocking application of said corresponding higher voltage thereto.

11. A system according to claim 10, wherein said correcting element comprises a transistor operatively connecting said diode and said first mentioned transistor to said winding, said threshold-value switch comprising a transistor operatively controlled by said thresholdvalue sensing means, said threshold-value sensing means comprising a Zener diode operatively connecting said winding to said threshold value transistor. 

1. A constant current source for the operation of multiple coil systems employing a static winding and at least one dynamic windings, effective at a common air gap, having a constant operational voltage source, a correcting element operatively disposed between the operational voltage source and the static winding, and a current system operative to control the correcting element, comprising a threshold-value switch, threshold-value sensing means operatively connected to the static winding and to the threshold value switch, a corresponding higher operative voltage source, said threshold-value switch being operative in the presence of subtractive voltages, induced in the static winding as a result of the presence of the dynamic winding, to connect the static winding with said higher corresponding operaTional voltage source over said correcting element.
 2. A system according to claim 1, wherein the higher operational voltage source is a separate independent operational voltage source.
 3. A system according to claim 1, wherein the higher operational voltage source comprises at least one capacitor circuited to be charged by the lower operational voltage, and associated switch means operatively connected to said threshold-value switch, operative, when the latter is actuated, to switch the charge voltage of said capacitor in series with the lower operational voltage source.
 4. A system according to claim 3, wherein a plurality of charged capacitors and associated switch means are provided and arranged for connection in series with said lower operational voltage, when said threshold value switch is actuated.
 5. A system according to claim 3, wherein said associated switch means comprises a transistor.
 6. A system according to claim 4, wherein said associated switch means for the respective capacitors each comprises a transistor.
 7. A system according to claim 6, wherein each of said capacitors is circuited to receive said lower operational voltage over an appropriately poled diode, the transistor comprising the switch means associated with each capacitor being operatively connected in series with such capacitor, and such capacitor and cooperable transistor shunting the associated diode, said diodes being operative, when the associated transistors are blocked, to supply the lower operational voltage to said correcting element and to the respective associated capacitors to charge the same, and, when the associated transistors are conductive, to prevent discharge of the associated capacitor other than in series with said operational voltage and said correcting element.
 8. A system according to claim 7, wherein said correcting element comprises a transistor operatively connecting said winding, over said diodes, to said lower operational voltage, said threshold-value switch comprising a transistor operatively controlled by said threshold-value sensing means, the latter comprising a Zener diode operatively connecting said winding to said threshold-value transistor.
 9. A system according to claim 1, wherein the threshold values switch comprises a transistor, and the threshold-value sensing means comprises a Zener diode.
 10. A system according to claim 2, wherein said independent higher operational voltage source is operatively connected to and controlled by said threshold-value switch, and a diode operatively connecting said correcting element to the lower operation voltage source for blocking application of said corresponding higher voltage thereto.
 11. A system according to claim 10, wherein said correcting element comprises a transistor operatively connecting said diode and said first mentioned transistor to said winding, said threshold-value switch comprising a transistor operatively controlled by said threshold-value sensing means, said threshold-value sensing means comprising a Zener diode operatively connecting said winding to said threshold value transistor. 